1. Field of the Invention
This invention relates to a method of manufacturing methacrylic acid by the oxidation of methacrolein and to an oxidation catalyst.
More particularly, this invention relates to a method of manufacturing methacrylic acid by oxidizing methacrolein with molecular oxygen or a gas containing molecular oxygen in the presence of steam, characterized by using a catalyst containing (1) palladium, (2) phosphorus, (3) antimony and (4) oxygen as the essential components and (5) at least one member selected from the group consisting of bismuth, lead, chromium, iron, nickel, cobalt, manganese, tin, uranium and barium as the optional component, and to the oxidation catalyst.
2. Description of the Prior Art
Numerous catalysts have heretofore been proposed for use in the synthesis of methacrylic acid to be accomplished by the oxidation of methacrylein in a gaseous phase.
Many of these catalysts prove to be deficient in activity. When the reaction using such catalyst is carried out at an elevated temperature in the hope of enhancing the total conversion, a decomposition reaction is encountered giving rise to large volumes of undesirable by-products such as carbon monoxide and carbon dioxide. Thus, the conversion yield of methacrylic acid is low. The catalysts which are disclosed in Japanese Patent Laid Open Publication No. 67216/1973 and Japanese Patent Laid Open Publication No. 61416/1973 and which provide relatively high activity and selectively, for example, contain phosphomolybdic acid or a salt thereof as the principal component.
Phosphomolybdic acid-based catalysts have a disadvantage in that the catalyst lifetime is short. Once they lose activity, these catalysts cannot be restored to activity through a simple treatment such as re-calcination. When the temperature of reaction or calcination exceeds 450.degree. C., they are abruptly degraded in catalytic activity, they are thermally unstable and thus, they are not necessarily suitable for use as catalysts on a commercial basis.
Further, conventional phosphomolybdic acid-based catalysts offer a notably short catalytic lifetime when the reaction is carried out at a particularly high space velocity.
From a commercial point of view, development of a catalyst capable of providing high reactivity and high selectivity at low temperatures and enjoying a long service life is highly desirable. Particularly desirable is the development of a catalyst which enjoys a long service life even when the reaction is carried out at a high space velocity.